In-mold decoration (IMD) involves inserting decorative coated/non-coated films into a molding tool followed by injection molding process. The decorative films are covered on the surface of injection parts, resulting in decorative effects. The pattern image on the back of decorative films is sandwiched between the decorative films and injection parts. Therefore, the pattern image shows long durability.
Since polymeric films such as polycarbonate (PC) and polyethylene terephthalate (PET) show poor scratch resistance property, hard coatings are normally required to protect the surface of polymeric films.
To protect the surface of decorative films, hard coatings to be applied on the surface are required to be resistant to scratch, abrasion and chemical attacks. In general, good surface properties require a high crosslink density of the coating. However, high crosslink density leads to poor formability of coated films. During the forming process of the coated film, the coating tends to crack.
To achieve both high formability and surface durability of coated films against scratch and abrasion, drying and UV curing of the coatings in two steps, before and after film forming process are applied. Such process is disclosed in U.S. Pat. No. 2009/0269568 A1, which describes coated films wherein the coating comprises a polyurethane acrylates and nanoparticles; another process comprising two UV curing steps before and after film forming process, is described in JP 2009062401 wherein the coating comprises a UV curing resin composition which has an acrylate and a methacrylate as a main component.
Moderate formability and surface durability of coated films are also required for some applications. Before the film forming process, the coating on the surface of films has been cured, which means no additional UV curing process is required after the film forming process. To show a certain level of pencil hardness of the coated films, both crosslink density of the coating and substrates chosen should be considered. Compared to formable hard coated PC films, formable hard coated PET films show higher pencil hardness. JP 2011088962 describes a UV-cured hard coated film comprising PET as substrate and a top coating layer, which contains (meth)acryloyl group-containing epoxy (meth)acrylate, JP 2009274378 discloses similar laminated films in which the UV-curing materials contain urethane acrylate and/or epoxy acrylate. The similar laminated films have also been disclosed in JP 2009220280 in which the UV-curing materials contain polyester acrylate/urethane acrylate. UV-curing materials with acrylate (3 or more function groups)/acrylate (1 or 2 function groups)/UV radiation hardening-type silicone resin/nanoparticles (20˜300 nm) have been disclosed in JP 2011126157.
However, formable hard coated PET films show some drawbacks in terms of forming accuracy and poor adhesion to the injection parts which restrain the application of formable coated PET films for housing application. On the other hand, formable hard coated PC films show better forming accuracy and adhesion to injection parts due to the mechanical and surface properties of PC.